1. Field of the Invention
The present invention relates to a stored program controlled switching system.
2. Description of the Related Art
Current stored program controlled switching systems employ a hard disk system as a huge memory device for storing a vast amount of data such as control program, subscriber information, tariff information and information concerning maintenance, operations and administration. In order to meet new services and features and cope with software imperfections, system file data are updated by downloading data from a storage device such as digital recording tape and magnetic optical disks. For maintenance purposes, the data stored in the hard disk system are routinely duplicated onto a backup system including digital recording tape and magnetic optical disks. Because of the enormous volume of data and the speed limitations imposed on the hard disk system, it takes a long time, typically several tens of minutes, to complete an updating or a duplicating routine. Much longer time (typically several hours) is necessary to duplicate data onto a newly installed standby storage system.
In order to minimize the routine work time, Japanese Patent Publication No. 9-135465 discloses a system in which an extra memory system is provided for exclusively storing updating information, which is compared with working data. If a mismatch is detected, the corresponding portion of the working data is replaced with the updating data. Another technique disclosed in Japanese Patent Publication No. 1-309493 also relates to a stored program controlled switching system in which a card reader is provided and memory cards are used as an external storage means to store program and system data. Data stored in each memory card is read by the card reader and downloaded onto the random access memory of the switching system. A further technique is disclosed in Japanese Patent No. 2630263 in which all system are duplicated by a pair of identical subsystems including the switching network, the central processor and the hard disk system. In the duplicated hard disk systems, identical data are stored and constantly checked against each other and one of the systems is used as a working system and the other is in a standby mode. If the working system fails, a mismatch will be detected and a flag is set up, and the system is switched over from the working to the standby hard disk system. When the failed system is restored and duplicated with the current working system, the mismatched portion of data is copied from the current working hard disk system into the restored hard disk system so that same data are stored in both hard disk systems.
However, the prior art techniques still require the use of digital recording tape or magnetic optical disks as an external storage system, which contributes to the system size. Additionally, since a number of different types of data are stored, it takes time during a fault finding and recovery process to identify such data types and locate the troubled portion. Furthermore, it is often necessary to replace a failed hard disk drive. In such instances, a new hard disk drive may be shipped over long distances. During shipment, the hard disks are subjected to unfavorable transport conditions which may cause damages.
It is therefore an object of the present invention to provide a stored program controlled switching system that allows efficient trouble shooting and efficient maintenance routine.
Another object of the present invention is to provide a stored program controlled switching system that reduces the system size by eliminating the need to provide bulky recording systems.
Still another object of the present invention is to provide a stored program controlled switching system that reduces shipment cost at low probability of damage which would otherwise occur during shipment of memory devices.
According to the present invention, there is provided a stored program controlled switching system comprising a first set of detachably mounted nonvolatile semiconductor memory devices for respectively storing data of different types including a control program, a second set of detachably mounted nonvolatile semiconductor memory devices for respectively storing the data of different types, and a main memory. A first controller is provided for operating the first set of memory devices in a working mode and operating the second set of memory devices in a standby mode, copying data from the memory devices of the working mode into the main memory and into the memory devices of the standby mode, and performing a switchover between the operating modes when trouble occurs in the first set of memory devices. A second controller operates the switching system according to the data stored in the main memory.